Wood contacting the ground or above ground wood that often gets wet, will typically be attacked by decay fungi and insects. With the exception of naturally durable species, such as cedar or redwood, wood in such applications is treated with a wood preservative, thereby increasing the longevity. The primary preserved wood product has historically been southern pine lumber treated with chromated copper arsenate (CCA). Most of this treated lumber was used for decks, fencing, and landscape timbers. There has recently been raised concerns about the safety and health effects of CCA as a wood preservative, primarily relating to the arsenic content but also to the chromium content. In 2003/2004, due in part to regulatory guidelines and to concerns about safety, there has been a substantial cessation of use of CCA-treated products. As a result, new wood preservatives have been developed. The new generation of copper containing wood preservatives uses a form of copper that is soluble. Known preservatives include copper alkanolamine complexes, copper polyaspartic acid complex, alkaline copper quaternary, copper azole, copper boron azole, ammoniacal copper citrate, copper bis(dimethyldithiocarbamate), copper citrate, and the copper ethanolamine carbonate. While the name might not suggest it, all have a nitrogen base that complexes the copper, e.g., ammoniacal copper, monoethanolamine copper, diethyleneamine copper, and so forth, and most formulations have carbonate ions to stabilize the complexes. When these formulations contact water having alkaline earth ions, e.g., calcium and magnesium, scale will form.
The problem of precipitate formation (scaling) is not unique to wood preservatives. Manufacturing processes utilizing water, water treatment facilities, households, among others have also been faced with the problem of scale formation. A typical solution to scale formation has been to employ a chemical agent and an absorbent material or surfactant to prevent or remedy scale deposits. For instance, U.S. Pat. No. 6,645,384 to Richardson et al. discloses the use of 2 phosphonobutane 1,2,4 tricarboxylic acid and a quad polymer having a polyacrylate/methacrylate base and 6 wt % sulfonated monomers (allyloxybenzenesulfonic acid and methallyl sulfonic acid) to prevent accumulation of mineral scale and corrosion. Similarly, U.S. Pat. No. 6,641,740 to Cornelius et al. discloses use of algins, polysaccharides isolated from algae, to remove scale deposits. Yet another example is U.S. Pat. No. 3,518,204 to Hansen et al. which discloses a method to control the rate of scale formation with compounds such as triglycollamic acid and polyacrylamide. Another approach has been to introduce a scale formation inhibitor, such as monofluorophosphate salts, as disclosed in U.S. Pat. No. 5,182,028 to Boffardi et al. While these approaches are optimal in their respective fields of use, they do not allow for sufficient precipitate inhibition in the field of wood preservatives.
Wood preservatives commonly comprise a second biocide that is efficacious against the copper tolerant organisms and other particularly troublesome species. The second biocide is often composed of a triazole group or a quaternary amine group or a nitroso-amine group. In practice the principal criteria for commercial acceptance, assuming treatment efficacy, is cost. Of the many compositions listed above, only a few soluble copper containing wood preservatives have found commercial acceptance, and each comprises either a copper monoethanolamine carbonate complex or an ammoniacal copper carbonate complex.
Typically, the wood preservatives are shipped and stored in concentrated form. The concentrate is therefore diluted with available water before use. The diluent water is usually ordinary municipal water or even stream water, both of which may contain calcium and/or magnesium. If the diluted wood preservatives contain calcium and magnesium above the solubility level of their respective carbonates, precipitates will form. Such precipitates are known as scales. In general scale formation occurs when solubility of a particular salt is exceeded.
Such precipitates (scales) are considered objectionable and problematic, as they can cause a stain on the wood (which would often be colored by the copper) and/or cause plugging of the wood during a pressure injection treatment. To prevent plugging and staining, scales and other presipitates are usually filtered out of the copper containing solution, a step that may add significant cost to the wood treatment process. Another problem with scale that can not be addressed by filtering is that scale can act like a sponge to strip an inordinate amount of copper and more particularly of the inorganic biocides from the wood preservation composition.
A method of preventing scale formation is needed.